RFR: JDK-8261034: improve jcmd GC.class_histogram to support parallel

[Hamlin Li]

On Thu, 4 Feb 2021 03:40:26 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Hi @Hamlin-Li 
>> I am not reviewer, but maybe you could add test for "parallel" in BasicJMapTest.java.
>
>>  I am not reviewer, but maybe you could add test for "parallel" in BasicJMapTest.java.
> 
> That test is for the `jmap` command, not the `GC.class_histogram` jcmd. As I pointed out, there are tests in `test/hotpot/jtreg/serviceability/dcmd/gc` that already test `GC.class_histogram`. That would be a better starting point.

@plummercj Hi Chris, I have a question which might not be related to the patch, my presubmit tests always failed on linux platforms, but I don't think the failure is related to my patch. Would you mind to share some point? I totally have no idea what's going wrong.
The error messages are as following:

E: Could not configure 'libc6:i386'. 
E: Could not perform immediate configuration on 'libgcc-s1:i386'. Please see man 5 apt.conf under APT::Immediate-Configure for details. (2)
Error: Process completed with exit code 100.

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PR: https://git.openjdk.java.net/jdk/pull/2379